6.3 Defence against disease Flashcards
What is are pathogens?
Pathogens are any living organism or virus that is capable of causing disease.
They can be living organisms such as bacteria and fungus or they can be non living viruses like HIV.
What is the 1st line of defense?
Skin
- Consists of a dry, thick and tough region composed predominantly of dead surface cells
- Secretes chemicals that lower external pH making it hard for fungus and bacteria to grow
- Provides a physical barrier against the entry of pathogens
- Provides protection against physical and chemical damage
- Blood clotting!
Mucous membranes + cillia
- Found in nasal passages
- Mucuous traps pathogens before they enter the body
- Once caught they can be expelled or swallowed and broken down
Blood clotting
If skin is cut, blood vessles are exposed to the outside environment which gives pathogens an opportunity to invade. However, cuts in skin are sealed by blood clotting.
- When a blood vessel is damaged, platalets move to the site and form a temporary plug with red blood cells
- The platalets then release clotting factors that set off a chain of reactions.
- An enzyme called thrombin is released by the clotting factor signal.
- Thrombin then converts fibrinogen into fibrin which creates a mesh of strands around the open area that catches more platalets and blood cells, ultimately sealing up the wound.
What is thrombin?
An enzyme that is released by the clotting factor signal (released by the platalets).
It converts fibrinogen into fibrin.
Blood clot formation in coronary arteries
Coronary thrombosis
Someone who has a buildup of plaque in their arteries could experience a negative effect of blood clotting.
- If the plaque ruptures and begins to bleed, clotting factors work to plug the opening
- This time the mesh of fibrin will stop the bleeding but completely block the coronary artery.
Causes and consequences of blood clot formation in coronary arteries
Causes:
- Smoking
- High blood cholesterol concentration
- High blood pressure
- Diabetes
- Obesity
- Sedentary lifestyle
Consequences:
- Heart attack
- Part of the heart is deprived of O2 and nutrients
- Heart does not pump blood efectively
What is the 2nd line of defense?
The innate immune system, which is non-specific and non-adaptive in its response.
A principle component of this line of defence are phagocytic white blood cells (phagocytes) that engulf and digest foreign bodies
- Non-specific: it does not differentiate between different types of pathogens
- Non-adaptive: responds to an infection the same way every time
What do phagocytes do?
They engulf and egest foreign pathogens through the process of endocytosis (phagocytosis).
Describe the process of phagocytosis
- Phagocytes engulfs a pathogen through endocytosis
- The pathogen is brogen down (digested) with enzymes found in the lysosome
- Pathogen fragments (antigens) may be presented on the surface of the phagocyte in order to stimulate the third line of defence
What is the 3rd line of defense?
The adaptive immune system, which is specific in its response.
Consists of lymphocytes which produce antibodies in response to particular pathogens
- It can differentiate between particular pathogens and target a response that is specific to a given pathogen
- It can respond rapidly upon re-exposure to a specific pathogen, preventing symptoms from developing (immunological memory)
How do lymphocytes produce antobodies in response to particular pathogens?
- When phagocytic leukocytes engulf a pathogen, some will present the digested fragments (antigens) on their surface
- These antigen-presenting cells (dendritic cells) migrate to the lymph nodes and activate specific helper T lymphocytes
- The helper T cells then release cytokines to activate the particular B cell capable of producing antibodies specific to the antigen
- The activated B cell will divide and differentiate to form short-lived plasma cells that produce high amounts of specific antibody
- Antibodies will target their specific antigen, enhancing the capacity of the immune system to recognise and destroy the pathogen
- A small proportion of activated B cell (and activated helper T cell) will develop into memory cells to provide long-lasting immunity
What is an antigen?
An antigen is a substance that the body recognises as foreign and that will elicit an immune response.
What is an antibody?
An antibody is a protein produced by B lymphocytes (and plasma cells) that is specific to a given antigen. Serves as a recognition site for the immune system.
What are the effects of HIV on the immune system
This virus targets T cells used by our adaptive immune system, and infects and kills them meaning that our third line of defense cannot work properly.
This leaves out body defenseless against pathogens that would normally not be a problem for our body to fight off.
- Without treatment, HIV can gradually destroy the immune system, causing health decline and the onset of AIDS.
Methods of HIV transmission
- Unprotected sex
- Breastfeeding
- Sharing needles
- Exposure to infection if you work in the medical field
- Blood or organ transfusions
